The present invention is generally directed to toner processes, and more specifically to aggregation and coalescence processes for the preparation of toner compositions. In embodiments, the present invention is directed to the economical preparation of toners without the utilization of the known pulverization and/or classification methods, and wherein toners with an average volume diameter of from about 0.5 to about 25, and preferably from 1 to about 10 microns and narrow GSD characteristics can be obtained. The resulting toners can be selected for known electrophotographic imaging and printing processes, including color processes, and lithography. In embodiments, the present invention is directed to a process comprised of dispersing a resin in the form of an aqueous latex prepared by emulsion polymerization comprised of suspended resin particles of from about 0.05 micron to about 1 micron in volume average diameter in water containing an ionic surfactant and optionally a nonionic surfactant, mixing this resin blend with two or optionally three pigment dispersions of different color prepared in water using nonionic dispersants or optionally an ionic surfactant of the same polarity as that employed to form the latex, adding to this blend an aqueous solution of countercharging ionic surfactant, or coagulant of a concentration from about 0.5 to about 5 percent of the weight of the resin component of the latex, thereby causing flocculation of resin particles and pigment particles, shearing this flocculated gel using a high shear in-line or batch homogenization device, followed by heating, below the glass transition temperature (Tg) of the resin, and stirring of the flocculent sheared mixture which is believed to form statically bound aggregates of from about 0.5 micron to about 10 microns comprised of resin, and pigments and adding additional ionic surfactant as a dispersion stabilizer to the formed aggregate dispersion after the desired particle size is achieved, thereafter heating above the Tg of the resin to generate toner particles with an average particle volume diameter of from about 1 to about 25 microns having a color that is controlled by the quantity of different colored pigments used in the blending stage. It is believed that during the higher temperature heating stage the aggregate particles fuse or coalesce together to form toners. In another embodiment thereof, the present invention is directed to an in situ process comprised of preparing a latex of suspended resin particles, such as PLIOTONE.TM., comprised of poly(styrene butadiene) and of particle size ranging from about 0.01 to about 0.5 micron as measured by the Brookhaven nanosizer in an aqueous surfactant mixture containing an anionic surfactant such as sodium dodecylbenzene sulfonate, for example NEOGEN R.TM. or NEOGEN SC.TM., and a nonionic surfactant such as alkyl phenoxy poly(ethylenoxy)ethanol, for example IGEPAL 897.TM. or ANTAROX 897.TM., and mixing into this resin a quantity of dispersed pigment, such as HELIOGEN BLUE.TM. or HOSTAPERM PINK.TM., dispersed in water containing an anionic surfactant as indicated herein. This resin-pigment blend is then coagulated by the addition of an effective amount of an aqueous cationic surfactant solution, and a surfactant such as benzalkonium bromide (SANIZOL B-50.TM.) can be selected and is appropriate for inducing coagulation. The viscous flocculated or gelled blend is homogenized utilizing a high shearing device such as a Brinkman Polytron, or in-line homogenizer such as the IKA SD-41 device, which on further stirring while heating below the Tg of the resin results in formation of statically bound aggregates ranging in size of from about 0.5 micron to about 10 microns in average diameter size as measured by the Coulter Counter (Microsizer II); and thereafter heating above the Tg of the latex resin to provide for particle fusion or coalescence of the polymer and pigment particles; followed by washing with, for example, hot water to remove surfactant, and drying whereby toner particles comprised of resin and pigment with various particle size diameters can be obtained, such as from 1 to 12 microns in average volume particle diameter. The aforementioned toners are especially useful for the development of colored images with excellent line and solid resolution, and wherein substantially no background deposits are present. While not being desired to be limited by theory, it is believed that the flocculation or aggregation is formed by the neutralization of the resin-pigment mixture by the added cationic surfactant. The high shearing operation ensures the formation of a uniform homogeneous flocculated system, or gel from the initial inhomogeneous dispersion which results from the flocculation action, and this uniform gel ensures the formation of stabilized aggregates that are negatively charged and comprised of the resin and pigment particles of about 0.5 to about 5 microns in volume diameter. Thereafter, heating is applied to fuse the aggregated particles or coalesce the particles into a toner or toners of a particular desired color. Furthermore, in other embodiments the ionic surfactants can be exchanged, such that the resin-pigments mixture contains cationic surfactant and coagulation is induced using an anionic surfactant solution; followed by the ensuing steps as illustrated herein to enable flocculation by homogenization, and form statically bounded aggregate particles by stirring of the homogeneous mixture and toner formation after heating. The latex resin particles, or blend of resin particles, used in the aggregation are chosen for their functional performance in the xerographic process, most particularly in that part of the process involved with fixing the image to the final receptor medium, most usually paper. This necessitates the process being accomplished with a latex prepared from a polymer resin with a controlled molecular weight and molecular weight distribution. As a result, the particle size and Tg of the latex for a toner application is fixed by the resin formulation process, usually emulsion polymerization, and this limits the means to make toners of different sizes from the same latex formulation. More specifically, the utilization of a constant latex surfactant to pigment dispersion counterionic surfactant ratio when aggregating the latex under differing solid loadings ensures a uniform chemical composition of the toner while also providing a means to obtain narrow size distribution toner particles.
In reprographic technologies, such as xerographic and ionographic devices, toners with average volume diameter particle sizes of from about 9 microns to about 20 microns are effectively utilized. Moreover, in some xerographic technologies, such as the high volume Xerox Corporation 5090 copier-duplicator, high resolution characteristics and low image noise are highly desired, and can be attained utilizing the small sized toners of the present invention with an volume average diameter particle of less than 11 microns and preferably less than about 7 microns, and with narrow geometric size distribution (GSD) of from about 1.2 to about 1.3. Additionally, in some xerographic systems wherein process color is utilized, such as pictorial color applications, small particle size colored toners of from about 3 to about 9 microns are highly desired to avoid paper curling. Paper curling is especially observed in pictorial or process color applications wherein three to four layers of toners are transferred and fused onto paper. During the fusing step, moisture is driven off from the paper due to the high fusing temperatures of from about 130.degree. to 160.degree. C. applied to the paper from the fuser. Where only one layer of toner is present, such as in black or in highlight xerographic applications, the amount of moisture driven off during fusing is reabsorbed proportionally by paper and the resulting print remains relatively flat with minimal curl. In pictorial color process applications wherein three to four colored toner layers are present, a thicker toner plastic level present after the fusing step inhibits the paper from sufficiently absorbing the moisture lost during the fusing step, and image paper curling results. These and other disadvantages and problems are avoided or minimized with the toners and processes of the present invention. It is preferable to use small toner particle sizes, such as from about 1 to 7 microns, and with higher pigment loading, such as from about 5 to about 12 percent by weight of toner, such that the mass of toner layers deposited onto paper is reduced to obtain the same quality of image and resulting in a thinner plastic toner layer onto paper after fusing, thereby minimizing or avoiding paper curling. Toners prepared in accordance with the present invention enable the use of lower fusing temperatures, such as from about 120.degree. C. to about 150.degree. C., thereby avoiding or minimizing paper curl. Lower fusing temperatures minimize the loss of moisture from paper, thereby reducing or eliminating paper curl. Furthermore, in process color applications and especially in pictorial color applications, toner to paper gloss matching is highly desirable. Gloss matching is referred to as matching the gloss of the toner image to the gloss of the paper. For example, with a low gloss image of preferably from about 1 to about 30 gloss, low gloss paper is utilized such as from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit, and, which after image formation with small particle size toners of from about 3 to about 5 microns and fixing, thereafter results in a low gloss toner image of from about 1 to about 30 gloss units as measured by the Gardner Gloss metering unit. Alternatively, if higher image gloss is desired, such as from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit, higher gloss paper is utilized such as from about 30 to about 60 gloss units, and, which after image formation with small particle size toners of the present invention of from about 3 to about 5 microns and fixing, thereafter results in a higher gloss toner image of from about 30 to about 60 gloss units as measured by the Gardner Gloss metering unit. The aforementioned toner to paper matching can be attained with small particle size toners, such as less than 7 microns and preferably less than 5 microns, such as from about 1 to about 4 microns, such that the pile height of the toner layer(s) is low.
Numerous processes are known for the preparation of toners, such as, for example, conventional processes wherein a resin is melt kneaded or extruded with a pigment, micronized and pulverized to provide toner particles with an average volume particle diameter of from about 9 microns to about 20 microns and with broad geometric size distribution of from about 1.4 to about 1.7. In such processes, it is usually necessary to subject the aforementioned toners to a classification procedure such that the geometric size distribution of from about 1.2 to about 1.4 is attained. Also, in the aforementioned conventional process, low toner yields after classifications may be obtained. Generally, during the preparation of toners with average particle size diameters of from about 11 microns to about 15 microns, toner yields range from about 70 percent to about 85 percent after classification. Additionally, during the preparation of smaller sized toners with particle sizes of from about 7 microns to about 11 microns, lower toner yields are obtained after classification, such as from about 50 percent to about 70 percent. With the processes of the present invention in embodiments, small average particle sizes of from about 3 microns to about 9, and preferably 5 microns are attained without resorting to classification processes, and wherein narrow geometric size distributions are attained, such as from about 1.16 to about 1.35, and preferably from about 1.16 to about 1.30. High toner yields are also attained such as from about 90 percent to about 98 percent in embodiments. In addition, by the toner particle preparation process of this invention, small particle size toners of from about 3 microns to about 7 microns can be economically prepared in high yields such as from about 90 percent to about 98 percent by weight based on the weight of all the toner material ingredients.
There is illustrated in U.S. Pat. No.4,996, 127 a toner of associated particles of secondary particles comprising primary particles of a polymer having acidic or basic polar groups and a coloring agent. The polymers selected for the toners of this '127 patent can be prepared by an emulsion polymerization method, see for example columns 4 and 5 of this patent. In column 7 of this '127 patent, it is indicated that the toner can be prepared by mixing the required amount of coloring agent and optional charge additive with an emulsion of the polymer having an acidic or basic polar group obtained by emulsion polymerization. Also, note column 9, lines 50 to 55, wherein a polar monomer, such as acrylic acid, in the emulsion resin is necessary, and toner preparation is not obtained without the use, for example, of acrylic acid polar group, see Comparative Example I. The process of the present invention need not utilize polymers with polar acid groups, and toners can be prepared with resins such as poly(styrenebutadiene) or PLIOTONE.TM. without containing polar acid groups. Additionally, the toner of the '127 patent does not utilize counterionic surfactant and flocculation process as does the present invention. In U.S. Pat. No. 4,983,488, a process is disclosed for the preparation of toners by the polymerization of a polymerizable monomer dispersed by emulsification in the presence of a colorant and/or a magnetic powder to prepare a principal resin component, and then effecting coagulation of the resulting polymerization liquid in such a manner that the particles in the liquid after coagulation have diameters suitable for a toner. It is indicated in column 9 of this patent that coagulated particles of 1 to 100, and particularly 3 to 70, are obtained. This process is thus directed to the use of coagulants, such as inorganic magnesium sulfate which results in the formation of particles with wide GSD. Furthermore, the '488 patent does not disclose the process of counterionic flocculation as the present invention. Similarly, the aforementioned disadvantages are noted in other prior art, such as U.S. Pat. No. 4,797,339, wherein there is disclosed a process for the preparation of toners by resin emulsion polymerization, wherein similar to the '127 patent polar resins of opposite charges are selected, and wherein flocculation as in the present invention is not believed to be disclosed; and U.S. Pat. No. 4,558,108, wherein there is disclosed a process for the preparation of a copolymer of styrene and butadiene by specific suspension polymerization. Other patents mentioned are U.S. Pat. Nos.3,674,736; 4,137,188 and 5,066,560.
In U.S. Pat. No. 5,290,654, the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toners comprised of dispersing a polymer solution comprised of an organic solvent and a polyester, and homogenizing and heating the mixture to remove the solvent and thereby form toner composites. Additionally, there is disclosed in U.S. Pat. No. 5,278,020, the disclosure of which is totally incorporated herein by reference, a process for the preparation of in situ toners comprising a halogenization procedure which chlorinates the outer surface of the toner and results in enhanced blocking properties. More specifically, this patent application discloses an aggregation process wherein a pigment mixture containing an ionic surfactant is added to a resin mixture containing polymer resin particles of less than 1 micron, nonionic and counterionic surfactant, and thereby causing a flocculation which is dispersed to statically bound aggregates of about 0.5 to about 5 microns in volume diameter as measured by the Coulter Counter, and thereafter heating to form toner composites or toner compositions of from about 3 to about 7 microns in volume diameter and narrow geometric size distribution of from about 1.2 to about 1.4, as measured by the Coulter Counter, and which exhibit, for example, low fixing temperature of from about 125.degree. C. to about 150.degree. C., low paper curling, and image to paper gloss matching.
In copending patent application U.S. Ser. No. 989,613 (D/92576), the disclosure of which is totally incorporated herein by reference, there is illustrated a process for the preparation of toner compositions, which comprises generating an aqueous dispersion of toner fines, ionic surfactant and nonionic surfactant; adding thereto a counterionic surfactant with a polarity opposite to that of said ionic surfactant; homogenizing and stirring said mixture; and heating to provide for coalescence of said toner fine particles.
In copending patent application U.S. Ser. No. 022,575 (D/92577), the disclosure of which is totally incorporated herein by reference, there is disclosed a process for the preparation of toner compositions comprising
(i) preparing a pigment dispersion in a solvent, which dispersion is comprised of a pigment, an ionic surfactant, and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a latex mixture comprised of a counterionic surfactant with a charge polarity of opposite sign to that of said ionic surfactant, a nonionic surfactant and resin particles, thereby causing a flocculation or heterocoagulation of the formed particles of pigment, resin and charge control agent to form electrostatically bounded toner size aggregates; and PA1 (iii) heating the statically bound aggregated particles to form said toner composition comprised of polymeric resin, pigment and optionally a charge control agent. PA1 (i) preparing a pigment dispersion in water, which dispersion is comprised of a pigment between 1 and 50 percent by weight and preferably between 5 and 25 percent by weight of the total dispersion comprising pigment, water, an ionic surfactant and optionally a charge control agent; PA1 (ii) shearing the pigment dispersion with a resin in the latex form prepared with an ionic surfactant of the same charging polarity to that used in formulating the pigment dispersion, a nonionic surfactant and then aggregating the resin-pigment blend using an aqueous solution of a counterionic surfactant; PA1 (iii) heating the resulting blend at temperatures between 20.degree. C. and 5.degree. C. about below the Tg, for example in the range of from between about 50.degree. C. and about 70.degree. C., to form statically bound aggregates of between 1 and 10 microns in average volume diameter with a GSD of between 1.10 and 1.30; then optionally adding additional ionic surfactant in a quantity of from between about 0.1 and about 2.0 percent by weight of the total suspension to stabilize the aggregates while they are subject to further heating to form coalesced toner particles in step (iv) below; and PA1 (iv) heating the statically bound aggregated particles at temperatures between 20.degree. C. and 45.degree. C. about above the resin Tg, for example in the range of from about between 50.degree. C. and 70.degree. C. to form the toner composition comprised of polymeric resin, pigment and optionally a charge control agent, the toner size being in the range of about 1 to about 12 microns in average volume diameter with a GSD in the range from 1.10 to 1.30 in embodiments.
Disadvantages associated with this process are that there is no way disclosed to obtain toners of different size utilizing the process of U.S. Ser. No. 022,575 (D/92577) the size of the toner being altered only by alteration of the starting latex resin size and composition and the quantity of coagulant added to form the aggregates. When toner particles are made by varying the coagulant/resin ratio the chemical composition of the obtained toner, particularly the surface properties of the toner can differ from one aggregate size to another, this can lead to critical differences in the xerographic behavior of the material as the xerographic toner charging process is very dependent on the toner surface chemistry.